1. Field of the Invention
The present invention relates to a thyristor having controllable emitter short circuits, and more particularly to a thyristor having a semiconductor body containing an exterior n-emitter layer provided with a cathode, an exterior p-emitter layer provided with an anode and two base layers respectively adjacent to the emitter layers, and having controllable emitter short circuits designed as metal-insulator-semiconductor structures arranged at a boundary surface of a semiconductor body, the controllable emitter short circuits comprising a respective first semiconductor region of a first conductivity type connected to the cathode, a respective semiconductor region of the first conductivity type connected to a base layer and an intermediate layer of a second conductivity type positioned between the latter regions which is covered by a gate electrically insulated with respect to the semiconductor body.
2. Description of the Prior Art
Thyristors of the type generally set forth above are known from U.S. Pat. No. 3,243,669. Upon the application of a control voltage to the gate of such a MIS structure, a short circuit path is activated which bridges the pn junction between the emitter layer connected to the cathode and the adjacent base layer. This results in a transfer of the thyristor from the current-conducting state into the block state in which practically no current flows between the cathode and the anode despite the voltage adjacent in the forward conducting direction. The change from the blocked state into the current-conductive state occurs by applying a further control voltage to the gate of a further MIS structure which bridges the pn junction between the two base layers in a low resistance manner.
On the other hand, a thyristor having a short circuit emitter is known from the German allowed application 24 38 894 in which an exterior emitter zone is penetrated by a plurality of short circuit zones to be interpreted as portions of the adjacent base layer, the short circuit zones extending up to the boundary surface of the thyristor body and being connected in the boundary surface to the cathode. Thereby, it is disadvantageous that several short circuit zones must be provided in order to achieve a good stability of the thyristor, i.e. a high security against unintentional triggering operations upon occurrence of voltages at the anode-cathode path poled in the forward conducting direction which partially increase very quickly (high dU/dt load). However, the triggering behavior is greatly influenced by a large plurality of short circuit zones. The trigger current required becomes large. The triggered surface of the thyristor spreads very slowly in the lateral direction over the entire cross section. As a result, significant turn-on losses occur.